The present invention relates to apparatus for forming cleat edges on sheet metal workpieces and more specifically to such apparatus in which the cleat edge is formed by a pair of wiping arms aft of and below a bending blade. The present invention is particularly addressed to the problem of forming cleat edges on one of the two panels of L-shaped duct sections previous to forming to the L shape, as well as to the problem of forming cleat edges on the side edges of duct pieces of greater length than the wiping arms.
Heretofore, complicated roll forming machines, such as the one shown in U.S. Pat. No. 3,815,398 to McClain, were utilized to perform these operations. With such apparatus, cleat edges could be formed on duct pieces of any desired length, and alternate portions of the workpiece edges could be cleated, leaving intermediate portions uncleated.
U.S. Pat. No. 2,973,796 to C. F. Engel, et al. discloses an apparatus for forming cleat edges on sheet metal workpieces by the use of a pair of wiping arms, one aft of and one beneath a bending blade. The wiping arms, their drive mechanism, and a rocker-arm type clamp for clamping the sheet metal workpiece relative to the bending blade are supported by vertical end plates at both sides of the bending blade. The clamp is driven by a tilt lever mechanism which extends forward at each side of the bending blade to circular tracks on heavy steel discs driven by the drive mechanism. Starting at a gaging position, against which the edge of the workpiece is first presented, the upper wiper arm turns to a clearance position, by which the cleated workpiece may be removed by an aft movement to free it from the bending blade, followed by upward and forward movement to remove the workpiece entirely. The wiper arm is then rotated the remainder of the 360.degree. revolution, returning it to the gaging position. Since the vertical end plates, drive mechanism and tilt lever lie at the ends of the bending blade, no clearance is provided for sideward projection of a workpiece from the wiping mechanism; a flat workpiece of greater length than the distance between the end plates cannot be cleated, nor may a cleat edge be formed on only one portion of a side edge of a workpiece except by first bending it upward at 90.degree. to fit in a space between clamping fingers. Thus, such prior apparatus does not permit insulating the interior surfaces of an L-shaped duct workpiece while flat. U.S. Pat. No. 3,994,152 to Wolters, though in most respects similar to the patent to Engel, discloses a slightly different way of both gaging and providing for removal of cleated workpieces. The cleat is formed during an unhalted 360.degree. revolution of the wiping arm; as it rotates from an initial position an expanding radius wiper arm portion directs the workpiece to be cleated to a gaging position. The cleat edge is then formed by continued rotation to the initial position, which now provides clearance, permitting the cleated workpiece to be removed by the same movements as in the patent to Engel.